Don't add rule feature data for rules which may never match.

Don't add rule feature data for rules which may never match.

:host and :host-context must always be in the rightmost compound with
no other simple selectors except a succeding pseudo element in order to
match as the host element is feature-less in that context. It's however
not an invalid selector according to the CSS Scoping spec, so we
shouldn't drop it at parse time.

We could potentially skip adding other selectors to rulesets as well
including selectors like:

:hover:not(:hover), div:not(div), ::content and ::slotted not in
shadow trees, etc.

R=kochi@chromium.org,ericwilligers@chromium.org
BUG=489481
Committed: https://crrev.com/6c4b4fbb5192fb3624d428172cdf916013bc5a2e
Cr-Commit-Position: refs/heads/master@{#376116}

[rune, 2016-02-17 13:28:26]

See dependency to other CL.

[rune, 2016-02-18 06:26:12]

The CQ bit was checked by rune@opera.com to run a CQ dry run

[commit-bot: I haz the power, 2016-02-18 06:26:20]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1703893002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1703893002/1

[kochi, 2016-02-18 06:56:05]

Sorry for the delay in reviewing, understanding which
rules to reject for :host/:host-context() was tricky 
(which is inherent to :host itself, anyway) - 
I should have looked at the unittest cases first :)

lgtm

[commit-bot: I haz the power, 2016-02-18 07:36:24]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2016-02-18 07:36:24]

Dry run: This issue passed the CQ dry run.

[rune, 2016-02-18 07:38:57]

The CQ bit was checked by rune@opera.com

[commit-bot: I haz the power, 2016-02-18 07:39:34]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1703893002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1703893002/1

[commit-bot: I haz the power, 2016-02-18 07:44:49]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-02-18 07:46:07]

Description was changed from

==========
Don't add rule feature data for rules which may never match.

:host and :host-context must always be in the rightmost compound with
no other simple selectors except a succeding pseudo element in order to
match as the host element is feature-less in that context. It's however
not an invalid selector according to the CSS Scoping spec, so we
shouldn't drop it at parse time.

We could potentially skip adding other selectors to rulesets as well
including selectors like:

:hover:not(:hover), div:not(div), ::content and ::slotted not in
shadow trees, etc.

R=kochi@chromium.org,ericwilligers@chromium.org
BUG=489481
==========

to

==========
Don't add rule feature data for rules which may never match.

:host and :host-context must always be in the rightmost compound with
no other simple selectors except a succeding pseudo element in order to
match as the host element is feature-less in that context. It's however
not an invalid selector according to the CSS Scoping spec, so we
shouldn't drop it at parse time.

We could potentially skip adding other selectors to rulesets as well
including selectors like:

:hover:not(:hover), div:not(div), ::content and ::slotted not in
shadow trees, etc.

R=kochi@chromium.org,ericwilligers@chromium.org
BUG=489481

Committed: https://crrev.com/6c4b4fbb5192fb3624d428172cdf916013bc5a2e
Cr-Commit-Position: refs/heads/master@{#376116}
==========

[commit-bot: I haz the power, 2016-02-18 07:46:08]

Patchset 1 (id:??) landed as
https://crrev.com/6c4b4fbb5192fb3624d428172cdf916013bc5a2e
Cr-Commit-Position: refs/heads/master@{#376116}

[esprehn, 2016-02-18 07:58:31]

Ideally this pre match would be outside RuleFeature so querySelector could use
it too and we could add simplify all the host matching logic in SelectorChecker.